1. Field of the Invention
The present invention relates to a television circuit utilizing a color burst signal. More specifically, the present invention relates to a television circuit which utilizes a color burst signal and is used in a color killer circuit, an ACC circuit, an APC circuit, and a color reproducing circuit or a television receiver which is provided with the circuits therein.
2. Description of the Prior Art
With referring to FIG. 20, in a conventional color killer circuit 1, a color burst signal and a sub-carrier signal are inputted to a multiplier 2, whereby an output according to the presence or absence of the color burst signal is applied to an LPF 3, and thus, a voltage signal V1 as shown in FIG. 21(A) is outputted for each horizontal line from the LPF 3. In addition, although such a voltage signal V1 has a time width, in FIG. 21(A), the same is illustrated as a line to simplify the illustration. This is also applied to FIG. 6(A) and FIG. 14(A).
A peak hold signal V2 shown in FIG. 21(B) is outputted from a peak holding circuit 4 to which the voltage signal V1 is applied, and a voltage signal V3 as shown in FIG. 21(C) is outputted from an LPF 5, whereby a color killer signal as shown in FIG. 21(D) can be outputted from a level-comparator 6. That is, in receiving a color television signal, the color killer signal of the high level is outputted as such, a color killer operation, is not performed. In receiving monochrome television signal, the color killer signal of the low level is outputted, and the color killer operation is performed.
In such a conventional color killer circuit 1, if a time constant of the LPF 5 is made small, there occurs an erroneous operation as follows: In a case where the voltage signal V1 is largely affected by a noise as shown in a period X in FIG. 21(A), the voltage signal V3 is also largely affected by the noise, and therefore, there occurs a period (a) (FIG. 21(C)) during which the voltage signal V3 becomes smaller than a reference voltage Vref in spite of a color television signal. Therefore, due to the influence of the noise, the color killer signal of the low level is outputted as shown in FIG. 21(D), and the color killer operation is erroneously performed.
On the other hand, if the time constant of the LPF 5 is made be large, since the peak hold signal V2 is more smoothed, and therefore, the voltage signal V3 is not made be small to a level that is lower than the reference voltage Vref; however, in a case where the television signal being received is changed from a color television signal to a monochrome television signal or vice versa, it takes a long time to switch the color killer signal, and therefore, there was a problem in that it is impossible to rapidly respond to the change of the television signal.